Deformation Uniformity Research Articles

Crushability maps for structural polymeric foams in uniaxial loading under rigid confinement

A family of epoxy-based polymeric foams with various initial porosity levels was subjected to quasi-static uniaxial loading in rigid confinement (uniaxial strain) to investigate their crushability characteristics. Two issues were investigated. The first issue was the uniformity of deformation in a specimen as a function of porosity level by creating a grid of equally spaced thin stripes on the surface and by monitoring their pattern during the experiment. It was found that the higher the porosity of foam, the more non-uniform the deformation in the specimen. However, the localized non-uniform deformation did not affect the global stress-strain response, especially at large deformations. The second issue was the development of a new analysis tool, called “crushability map”. The purpose of the tool is to depict the evolution of porosity, bulk density and energy absorption as functions of applied strain, stress, and porosity. These maps can assist in characterizing the residual crushability or energy absorption capability of foams as a function of residual porosity. The maps can be used as a design tool for selection of suitable foams for a given application in conjunction with various design criteria.

Finite Element Investigation of Equal Channel Angular Extrusion Process

In this study, the effect of material properties on deformation pattern and strain distribution of the commercially-available pure titanium (CP-Ti) specimen during an equal channel angular extrusion (ECAE) was investigated. Finite element analyses were carried out for two-dimensional plane strain condition at elevated temperatures. Material properties were assumed by hardening, softening, and no hardening behaviors based on the measured experiment data. The effects of friction conditions, die geometries, and processing routes were also examined under the same processing condition. Based on the value of average strain and standard deviation of the strain distribution, the magnitude and uniformity of deformation was determined depending on process conditions. In addition, damage parameters based on plastic work and Cockroft and Latham criteria were calculated to check the likeliness of surface cracking. Finally, non-isothermal analyses were carried out to explore the effect of processing temperature in the ECAE process.

Effect of Aging on Fatigue-Crack Growth Behavior of a High-Temperature Titanium Alloy

The effects of aging on the room-temperature fatigue-crack growth (FCG) behavior of a newly developed high-temperature near-a titanium alloy (Ti-5.6Al-4.8Sn-2Zr-1.0Mo-0.32Si-0.8Nd) with both bimodal and lamellar microstructures were investigated. The results indicate that aging had a relatively small effect on the FCG behaviors of the concerned alloy. The effect of aging is more pronounced on the lamellar than on the bimodal microstructure. This effect reduces with aging time especially for the lamellar microstructure. TEM and SEM studies were performed to gain insight into the deformation behavior and crack propagation mechanisms of the alloy. Dependence of the FCG rates on aging treatment is rationalized by considering changes in crack path tortuosity, roughness-induced crack closure and deformation uniformity. Slip reversibility is also considered. The work suggests that the amount and size of alpha(2) particles based on Ti3Al is mainly responsible for this dependence in the high DeltaK range.

Preform die shape design for uniformity of deformation in forging based on preform sensitivity analysis

A finite element based sensitivity analysis method for preform die shape design in metal forging by controlling the deformation uniformity is developed in this paper. The optimization problem is to minimize the effective strain variation within the final forging through optimizing the preform die shape, so that a more uniform deformation within the final forging can be obtained. The preform die shapes are presented by cubic B-spline curves. The control points of the B-spline curves are used as the design variables. The objective function expressed by the effective strain variation is constructed. For two-dimensional forging problems, the sensitivity equations of the objective function, elemental volume, elemental effective strain-rate and the elemental strain-rate with respect to the design variables are developed. The optimization procedures of the method are given. The preform die shapes of two H-shaped forging processes in axisymmetric and plane-strain deformation are designed using the method.

Processing issues for high critical current density in BSCCO-2212 composites

Issues for controlling the critical current density (J/sub c/) in long tapes and wires include homogeneity of the starting powders, optimization of the ceramic size and shape, uniformity of the deformation or coating processes, and control of the heat treatment parameters. This range of issues is discussed for both multilayer dip-coated and multifilamentary powder-in-tube composites. In particular, J/sub c/ is shown to depend strongly on ceramic size and shape. Continuing efforts to correlate J/sub c/ with processing issues are presented. Progress toward applications in high field coils is described.

Constitutive testing of Red Wildmoor sandstone

The first objective of this research was to improve the experimental measurements for the constitutive behaviour of Red Wildmoor sandstone by optimizing the boundary conditions and specimen geometry, and improving the triaxial test instrumentation. The uniformity of deformation of the rock specimen was improved by minimizing specimen bulging due to specimen slenderness and end-surface frictional constraints. The improvements in the instrumentation were aimed at improving the monitoring of the applied forces, axial and radial deformations, and macroscopic rock failure through use of high precision LVDTs and cantilever gauges, acoustic emission measurements and acoustic pulse transmission velocities. The second objective was to obtain test data for the constitutive modelling and calibration of Red Wildmoor sandstone under various saturating conditions and saturation fluids. An additional task was an experi mental study for the improvement of the uniaxial compression test as an index text for rock mechanics applications. The performed modifications allowed the reliable collection of post-peak stress test data of material softening behaviour, and the identification of the point of macroscopic failure of the specimen beyond which the test data cannot be used directly for continuum modelling of material behaviour. © 2000 John Wiley & Sons, Ltd.

Stress relaxation behaviour in bending of high strength copper alloys in the Cu–Ni–Sn system

The microstructure of spinodally hardened, stress relaxation tested Cu–Ni–Sn alloys is characterized. The main mechanism of relaxation is recrystallization. At 150°C, initial stress values of 480–600 N mm −2 cause significant microstructural changes even if up to 90% of the initial stress remains after 1000 h of testing. Elevated temperature stability depends on the uniformity of deformation.

Effect of the degree of defectiveness of an original material on the deformation structure formed in the explosive collapse of thick-walled hollow cylinders

The effect of shock-wave preloading on the formation of a deformation structure in copper and tantalum upon subsequent high-velocity plastic deformation performed by the method of explosive collapse of a hollow thick-walled cylinder has been studied. Prehardening is shown to favor the structural uniformity of deformation up to large values owing to creation of a highly disperse intragranular structure.

Methodology and apparatus to determine material properties of the knee joint meniscus

This paper describes a soft tissue test method and apparatus which determines the constants necessary to characterise the elastic properties of a transversely isotropic material such as the knee joint meniscus. The tensile machine was designed to test small delicate samples in a humidified environment and measure specimen deformation with a CCD video camera. The method described here employs a common specimen preparation procedure and test protocol using specimens with four different fibre orientations. Discrete markers (0.075 mm graphite particles) permit repeatable measurements of two-dimensional strain on the specimen surface enabling the determination of Poisson's ratio characteristics. Shear strain was also measured in tensile test specimens prepared with an oblique collagen fibre orientation, offering an alternative method to investigate shear properties. Regional strain measurements provide an assessment of the uniformity of the tissue deformation. Preliminary results on bovine menisci are presented as an application of the test system. Material properties characterising the meniscus tissue were obtained with one test procedure and identical coupon size. This has the advantage of avoiding systematic errors caused by different preparation techniques, test procedures and equipment.

Determination of flow stress by inverse solution using finite element method

A newly developed method to determine flow stress of a material has been proposed. This method, named FC-method, is an application of inverse analysis. Since FC-method does not need uniformity of deformation which is the requirement for conventional methods such as uniaxial tensile or compression test, flow stress of a material expressed as a function of unknown material constants is obtained with good accuracy up to large strain range. FC-method employs, as the object function of inverse analysis, the balance of external and internal powers which are given to a material during a deformation process and spent for the deformation respectively. The external power is obtained from the load-displacement curve measured and the internal power is calculated through FEM analysis of the deformation. Then optimization of the balance through inverse analysis gives flow stress of the materia. Friction coefficient between the material and the tools for deformation is also one of the unknown constants and determined through FC-method simultaneously with flow stress. The object function of FC-method explicity contains unknown constants to be determined, therefore the cost of the analysis to obtain flow stress is reduced. Numerical study to verify FC-method was carried out using ring compression problem of type 304 stainless steel between two parallel plane dies, which clarified that FC-method was effective.

The Influence of Mo on the Physical and Mechanical Properties of Single Crystalline Nial

AbstractThe room and elevated temperature (300°C and 600°C) tensile properties of single crystalline NiAl with and without molybdenum additions have been investigated. It is shown that 0.2at% molybdenum has a considerable influence on the mechanical properties of NiAl and this influence is sensitive to heat treatment. At room temperature, the ductility of the Mo-doped alloy was higher than the binary NiAl after appropriate heat treatment. Furthermore, the elongations observed are highest at 300°C and are related to greater uniformity of deformation.

An innovative strategy for open loop control of hot deformation processes

A new strategy for systematically calculating near optimal control parameters for hot deformation processes is presented in this article. This approach is based on modern control theory and involves deriving state-space models directly from available material behavior and hot deformation process models. Two basic stages of analysis and optimization are established in this strategy for nonlinear, open loop control system design for producing required microstructural characteristics, uniformity of deformation and temperature distribution, and other important physical requirements of hot worked products.

Non‐uniformity of two‐dimensional myocardial deformation in response to chronotropic and inotropic stimulation in cats

The degree of uniformity of myocardial deformation for cross-oriented segments in the anterior wall of the left ventricle is influenced both by loading conditions and by infusion of isoprenaline. The aim of this study was to clarify the chronotropic influence (atrial pacing) compared to the combined inotropic and chronotropic effects of isoprenaline on uniformity of contraction. In eight open-chest pentobarbitone-anaesthetized cats segment performance was measured by orthogonal sonomicrometry. Heart rate (HR) increased from control state, 199 +/- 5 (mean +/- SEM) beats min-1, to 224 +/- 6 and 227 +/- 7 beats min-1 during atrial pacing and isoprenaline infusion, respectively (P < 0.0005). Circumferential segment shortening remained unchanged during pacing but increased with isoprenaline (P < 0.0005). Longitudinal segments showed reduced shortening during pacing (P < 0.05), whereas shortening during isoprenaline infusion did not differ from control shortening. The ratio between shortening of longitudinal and circumferential segments, long/circ ratio, changed from 0.52 +/- 0.13 in the control state to 0.36 +/- 0.10 during pacing and 0.39 +/- 0.11 with isoprenaline (P < 0.05). End-systolic pressure-length relations were unchanged by atrial pacing but showed leftward shifts during isoprenaline infusion. Myocardial tissue blood flow (microspheres) was unchanged during interventions. We conclude that both atrial pacing and isoprenaline infusion lead to a more non-uniform deformation in the anterior wall. However, non-uniformity during atrial pacing was primarily related to reduced longitudinal shortening whereas the non-uniformity during isoprenaline infusion was due to increased circumferential shortening.

Cyclic cracking resistance of low-alloy and carbon structural steels hardened by tensile deformation and heat treatment

Cold drawing deformation of structural steels increases the yield limit of the material while retaining sufficiently high ductility and toughness. Consequently, in a number of cases the users of constructional rolled metal stock give preference to hardening by cold drawing in comparison with thermal hardening. This treatment is applied to, in particular, low-alloy structural steels. Taking into account the large volume of production of these steels, it is easy to see that the production of material with high strength by this method is associated with a high consumption of scarce alloying elements. In the USSR, attempts were made in recent years to examine the process of cold deformation of standard low-alloy steels strengthened by heat treatment and the possibilities of increasing the strength of structural rolled metal stock from these steels, already subjected to preliminary thermal hardening. At the same time, there are almost no reports on the susceptibility to brittle failure after these treatments, evaluated by fracture mechanics criteria. Hardening reinforcement bars by cold drawing has a strong effect on the cyclic cracking resistance of the material, in particular on one of the most important characteristics, i.e., the growth rate of fatigue cracks. In this case, the effect of cold deformation on this parameter is ambiguous: the fatigue crack growth rate can either decrease or increase, or remain unchanged in comparison with its value in the steel in the undeformed condition [1-5]. It is also necessary to explain the problem of the behavior of a fatigue crack in cold-deformed metal, whose properties change during cyclic loading. The importance of these interrelationships for practice is evident since the capacity of the material to resist brittle failure determines in the final analysis the service life of the structure. The aim of this investigation was to obtain such data for reinforcement steels of a periodic section, and carry out comparative analysis of the variation of the properties during cyclic of loading hot-rolled and thermally hardened cold-deformed steels. Hardening these steel bars by drawing was carried out by cold tensile deformation of reinforcement rods of a periodic section 850 mm long. Tensile loading was carried out in an EUS-100 hydraulic testing machine with the travel speed of the moving clamps of 5 mm/min. The degree of plastic deformation was inspected using an Amsler mechanical strain gauge with the measurement length of 40 mm and a scale divided in 0.01 mm. The uniformity of plastic deformation was evaluated on the basis of simultaneous readings of two strain gauges fixed at the ends of the gauge length. The measurement results show that the nonuniformity of plastic deformation along the length of the rod does not exceed + 5 %. The reinforcement rods, hardened by cold drawing, were then tested by static tensile loading to determine the standard mechanical characteristics (ultimate strength, physical yield limit or proof stress, relative uniform and relative elongation). The experiments were carried out on specimens 450 mm long in the same EUS-100 testing machine. Cyclic cracking resistance was evaluated by constructing the diagrams of fatigue failure (FFD) in cantilever bending of prismatic specimens 8  16 x 60 mm in size with a side notch at a loading frequency of 11 Hz and a stress ratio of R=0. The length of the fatigue crack was measured by the method of the electrical difference of the potentials with automatic recording of the relevant parameter. The measurement error of the length of the fatigue crack did not exceed 6% and that of the force was not higher than 9%.

Heat treatment of commercial titanium

Knowing the temperature-time dependence of internal friction, the finely dispersed condition of VT1-0 commercial titanium can be fixed by quenching from the temperature of the α →β transformation and the yield limit of the cold-worked material can be greatly reduced. It is evident that the reduction of the residual relative reduction of the area of the cross section in the neck (ψ) is associated with an increase of the uniformity of deformation. It is useful to carry out further detailed examination of the suitability of the method of heating titanium in the salt melt for processing purposes.

An apparatus for the study of molecular monolayers compressed at the air-water interface with uniform shear

An apparatus is described that has been designed to compress monolayers with homogeneous shear. It consists essentially of a rectangular frame with hinges at the corners that can fold to form a parallelogram. It is supported at the interface by two rods which can rotate, one of which is controlled by an electric motor acting on a pantograph. This enables the area enclosed by the frame to be decreased linearly with time. The apparatus has been tested by observing the uniformity of deformation of a square grid of lines of sulphur powder applied to a condensed monolayer. One application of this apparatus is in the preparation of uniformly oriented films of polymer for research and technical purposes. This is illustrated by the high dichroism of the polarized IR spectrum of poly( L-alanine) formed from a compressed monolayer.

Al-Cu合金系超塑性材料の&lt;I&gt;m&lt;/I&gt;値の引張り速度比依存性

The strain rate sensitivity index, m, of Al-33Cu and Al-27Cu-5Si alloys was measured by the two methods, (a) the differential closs-head speed method and (b) the strain rate change method. The m-value by the method (a) was dependent strongly on strain and decreased with increasing strain. The m-value by the method (b) was dependent slightly on strain, but strongly on the width and the sense of the change from a given strain rate, \dotε1, to another one, \dotε2. The dependence of m on the width, J∗=∂m⁄∂\sqrt(lnN)2 where N=\dotε2⁄\dotε1, was positive or negative depending on whether the strain rate was lower or higher than the strain rate having the maximum m-value on the m-ln\dotε curve when N=2 (the reference curve of m). At the strain rate having the maximum m-value, the value of |J∗| showed the minimum value (|J∗|∼0). Since the m-value is defined by the strain rate and strain rate change, it is desirable to measure m by the method which excludes the effect of strain on flow stress, and it is suggested that the strain rate change method is the one in accordance with the definition. When specimens were deformed under the condition of the same m-value on the reference curve of m, the fracture strain and the uniformity of deformation in the strain rate region where J∗>0 were higher than those in the region where J∗<0.

Properties of 10R6M5-MP steel produced by rolling

1. The use of hot rolling for production for powder metallurgy high-speed steel provides the possibility of production of high-density compacts not inferior in the level of mechanical properties to standard steel. 2. With close values of mechanical properties of powder metallurgy and standard high-speed steels defects related to the preparation and working of the original powder have the dominant influence on the level of service properties. 3. The basic directions in further improvement in the properties of the powder metallurgy steel are an increase in the quality of the powder and in the uniformity of deformation in working of it by pressure.

Al-33Cu超塑性合金における不均一形状試料の変形挙動

Tensile tests were carried out to investigate deformation behaviours of specimens with various shapes of pre-existing non-uniformities. The results are summarized as follows: (1) The deformation behaviours of the specimens depend not only on the initial ratio of minimum/maximum cross-sectional area (initial inhomogeneity factor α0) but also on the initial length of non-uniform region (l0). The reduction of the inhomogeneity factor with strain increases with increasing l0. (2) It is observed that the area-reduction rates of non-uniform region to that of uniform region (\Dot{A}n⁄\Dot{A}u) is less than 1 even if m<1, which is contrary to the expectation from the Backofen’s or the Hart’s analysis where \Dot{A}n⁄\Dot{A}u>1 for m<1. (3) It is shown that ΔA (the difference in cross-sectional area between uniform and non-uniform region) and Δ\Dot{A} cannot be connected directly with the uniformity of deformation. Therefore, it is not reasonable to use the Hart’s parameters for the evaluation of uniformity of deformation. (4) The boundary between non-uniform and uniform regions moves like Lüder’s front during deformation, which suggests strong force to act on the boundary. (5) It is pointed out that the fracture strain is controlled by the final value of α, the fracture diameter Df and the length of necking l0, so that the importnat is to find out the effects of m-value on α, Df and l0.

Superplastic isothermal forging: A model metal flow study

The isothermal forging of nickel and titanium alloys under superplastic conditions to produce close-to-form components is an emerging industrial process that can lead to much reduced component costs compared with conventional closed-die forging and machining techniques. Studies of the metal flow behaviour during forging under such consitions are important because of the need to ensure good die-filling, uniformity of deformation and control of local strain rates in the deforming workpiece. Such studies are experimentally difficult because of the high temperatures involved, and the approach taken in the present work was to use a model material, the tin—lead eutectic alloy, which is superplastic at ambient temperatures and allows the visioplasticity technique for analysing the flow This model approach has enabled the mechanics of flow during the isothermal forging of a radial compressor wheel to be studied as a function of the preform geometry. The results show that good die-filling, especially in the blade areas, is promoted by decreasing the perform diameter and by the use of a preform chamfer, whereas larger diameter preforms lead to an improved uniformity of metal flow and a reduction in forging time. A critical preform geometry has been defined beyond which a mechanical instability occurs during forging with subsequent internal defect formation. This study has allowed the specification of an optimum preform geometry which is applicable to the isothermal forging of compressor wheels in the high-temperature nickel- and titanium-base alloys. This model approach to the study of the flow behaviour during isothermal forging of high-temperature materials is advantageous in two respects. Firstly, it allows optimisation of the preform geometry in the context of obtaining good die-filling and uniformity of the deformation (which reflects itself in the homogeneity of mechanical properties in the component). Secondly, through quantitative analysis of local strain rates during forging, it enables the specification of the forging press speed schedule so that the important areas in the deforming workpiece remain within the superplastic strain-rate range.